Tire Pressures for AutoX

cossie1600

The optimal temperature on a tire will vary based on the tire compound you are running. R comps will run at a much higher temp than any street tire. The general rule of thumb is a 10-20F warmer on the inside than any other. Of course this means you have to have camber adjustment. Also temperature should be taken after car comes off the track without a cool down lap. Lastly, never bleed your tires when it is hot as they will drop right back down as soon as the tires cool down.

VQStryker

yea, do not EVER bleed your tires when hot. haha, you'll end up with very low tire pressure after the car sits.

AutoX Z

Some people use chalk on the sidewall of the tire to see how much the outside shoulder of the tire is touching the ground. It's a simple way of making sure you're not running WAY too low pressure but not really much of a tuning tool beyond that.

Tire temperatures can be used to tell you which parts of tire is actually touching the ground and doing most of the work to make the car turn. When checking temperatures you want to make sure there is an even distribution from the inside to the outside of the tire. This is usually done by taking a reading at three points (Inside Middle Outside). You want to see some type of linear distribution between these two points with the middle falling in between the inner and outer temperatures. If the middle is lower, you need to increase pressures; if the middle is higher, you need to lower pressures.

Temperature data can also be used to set the camber. If the outside is much higher than the inside you need more camber and if the inside is much higher you need less camber.

Keep in mind all of this applies if you are trying to optimize the grip of the tires. In some classes, like stock, with limited tuning options you may purposely compromise the grip at one end of the car in order to change the handling characteristics.

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SPOHN

Thanks. Repped. You to cossie

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AutoX Z

Also I always check my tire pressure immediately after I come off course. That pressure is what the tire will actually be at while on course.

That being said it doesn't really matter when you check them as long as you're consistent in way you measure.

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AutoX Z

This really isn't true at least for auto-x compounds. Almost every street tire save maybe toyos are more heat tolerant than A6's.

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SPOHN

I did do that last time. Each run I was pushing it harder and it would increase tire pressure another 1-2lbs higher. Only on two runs after that it was set.

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cossie1600

I meant their operating temp at max. adhesion, not heat tolerence.

wstar

FWIW just going by very rough chalk and temps, last time out on road course stuff I ended up being around 31-32 PSI "cool" (after a cooldown lap and 10-15 unavoidable minutes sitting before I could check and adjust, I'm guessing it's about 37-38 hot based on previous checks), and that seemed to be using up the surface of the tire and not rolling over, on street Conti DW's, and at my relatively tame level of skill. In previous runs I've tried going higher than that, but around 35-36 under the same conditions (low 40's hot) the car just felt too bouncy and unstable.

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///MSH

From what i've seen here, it seems there are more road course guys than AutoX Guys...this might be an interesting poll.

In any case ...this thread is full of good advise. I will add a few bits that I haven't seen already discussed that i believe to be relevant factors. All in all, i think there are too many variables to answer the question cart-blanc.

You need to consider your track surface - it is just as relevant as the tire compound. I will run higher pressures on a surface will more grip.....generally speaking concrete has more grip than asphalt. Similarly, sealed asphalt is different than unsealed....you get the picture.

You need to adjust based on the course layout - Just as most people think about F/R differentials, you need to look at L/R. most autoXes, like road courses are either CW or CCW....as such you will see your pressures change from side to side.

I agree with those who use the factory marks that point to the edge of the tire. I take this a bit further. I use the marks on the front. And tune the real relative to the front depending on whether the track puts my car into a natural understeer or oversteer condition...if you think in extremes...the F/R differential is not unlike adjusting swaybar stiffness. Anyway, I say "natural" because throttle-endused oversteer can be fast or slow depending on when/how the driver chooses to employ it. When looking F/R, on tight asphalt courses, i have found that low thirties work well with about 1PSI more pressure up front.

As a passing thought, i subscribe to taking pressures/temperatures when i come off course only because i believe this is more indicative of what the temps/pressures will be when i'm on course. Also, specific to termperatures, I have found that R-Compounds will retain the heat longer than 140 or 180 treadware tires.....the point, if you have street tires, you'd better measure temperature quickly or the tread surface has alreay cooled down significantly.

Hopefully these thoughts will give you more to think about.

Cheers